AR-15, M4, M16 and similar prior art MILSPEC rifles cannot be quickly disassembled and reassembled where the rifle barrel connects to the upper receiver, a process which usually requires the use of specialized tools and a work-bench equipped with a vise. While there are some prior art systems that allow for in-field tool-less disassembly and reassembly of the barrel from the upper receiver, these systems are not effective or robust, are complicated to use, and do not allow for use of standard MILSPEC had guards and other accessories commoly used with these types of firearms.